Here's a thought experiment. Suppose the Washowski brothers decided now, in the year 2009, that The Matrix should have a subtitle, like Reloaded and Revolutions do.
They decide to call it The Matrix: Revelations because there's were the nature of the Matrix is revealed among other things.
Would you refer to The Matrix as "Revelations"? That should tell you everything you need to know about Star Wars vs. A New Hope.
P.S. I just want to mention one good example that illustrates my point:
Halo: Combat Evolved is usually called Halo, despite the potential for confusion with Halo 2 and Halo 3. We could call it Combat Evolved, esp. with Halo 3: ODST and Halo: Reach coming out soon, but we don't. Why? Probably because its a terrible name and there was no need to use it until 2004 but why change then since its clear Halo 2 is "Halo 2" and Halo is "Halo."